Measurement of Steam-Water Flows for the Total Flow Turbine

Hot water geothermal fields discharge steam-water mixtures, which have proved difficult to measure compared with the dry steam from fields like The Geysers and Lardarello. Hot water geothermal fields discharge steam-water mixtures, which have proved difficult to measure compared with the dry steam from fields like The Geysers and Lardarello. With the development of the lip pressure method, however (James 1962), an accurate method was derived which could measure the flow when a geothermal well discharges to the atmosphere at sonic velocity. Fortunately most discharges from wells do in fact attain such velocities, and as long as the enthalpy of the mixture is known, the flow can be determined. Where the enthalpy is unknown some other measurement has also to be made in order to solve the two factors of flow and enthalpy. By discharging the whole mixture into a silencer, the water portion can be estimated by means of a weir, and this provides the second measurement (described in James 1966) required to solve both unknowns. With the hoped-for commercial success of the total energy turbine in the near future, it will be necessary to have a means of measuring the steam-water flow into the machine. As long as the enthalpy of the flowing fluid is known, there should be no intrinsic difficulty in obtaining this, as the nozzles themselves act as metering devices due to the phenomena of sonic velocity at the throat. High gas concentrations in the steam phase, together with high chemical content in the water phase, require the use of “corrections” which will have to be determined from field tests to confirm theory. Clean steam-water mixtures appear to present no difficulties. 7 refs